Interoffice telephone



Ju1ys,1941. H. R. sHArw' f v'2,248,589

INTERQFFIQE .TELEPHONE Filed May 14o Inventor:

` Huber-t, F2. Shaw,y by JV 7J Patented July 8, 1941 INTEROFFICE TELEPHONE Hubert R. Shaw,v Drexel Hill,'Pa., assignor toGeneral Electric Company, a corporation of New York Application May 23, 1940,Serial N0. 336,757

4 Claims. (Cl. 179-387) My invention relates to communication systems and, while not limited thereto, it is particularly useful in interoice telephone systems.

In certain systems having no central switching station and providing for private communication between any pair of a number of stations, an individual circuit is provided'between each station and each of the other stations. When the system is not in use, the telephone apparatus at each station is normally connected tov every circuit leading thereto. To assure private conversation between two stations, it is necessary first for a calling station to disconnect its telephone apparatus from all circuitsV except that leading to the desired station, and second, after a call from the calling station, for the operator at the desired station to disconnect its telephone apparatus from all circuits but that leading to the station at which the call originated. It is an object of my invention to provide'a communication system having no central switching station and-having a minimum number of interconnecting circuits when the system includes a small number of stations, whereby a private communication may be made to a desired station without any action on the part of ran operator at the desired station.

It is a further object of my inventionto enable one to make a private communication to a desired station on a system havingan individual tionV may be transmitted to a desired station and may be prevented fromy being transmitted elsewhere at the option ofthe operator at the transmitting station. f

The features of my invention whichl I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with iurther objects 4and advantages thereof may best be understoodY by reference to the following description taken in connection with the accompanying drawing, in which Fig.` 1 is a circuit diagram illustrating an interoice communication system embodying my invention, and Fig. 2 is a detailed view in perspective of a portion of the apparatusy indicated in Fig. 1.

Referring to Fig. 1, there is shown a communication system including three stations A, B. and C. Each of these stations includes identical apparatus comprising-a telephone and, am-

pliiier device, and switching apparatus. Between each station and each vof theother stations there is a communicating circuit. These circuits comprise wires I0 and II co-nnecting stations A and B, wires I2 and I3 connecting stations A andC, andV wires I4 and I5 connecting stationsB and C. It-is understood, ofl course, that, if there are more than three stations in the system, .there must be Vprovided additional circuits.

Since the apparatus in each station is identical with that ineveryv other station, only the apparatus in station A will be completely described. The telephone and amplifying apparatus at station A'comprises a dynamic speaker yIB having a voice coil Il,V a reversing switch I8, and an amplifier I9. These devices are arranged for translation of sound into electric energy .which 4is amplied and transmitted Vthrough wires 20 and 2| to the switching apparatus corresponding tofstation- A and for translation of electric energy into sound, the energy being received from the switching apparatusV through wires 20 and 2| by Athe amplifier I9 and translated into sound by the speaker I6. l

A'dynamic speaker whose'voice coil moves in a xed magnetic eld produced by either a. permanent magnet or an electromagnet is a sound translating device whichrequires substantially more electric energy to producea given amount oi sound than it can generate whenexcited by the same vamount of-sound. That is, if anelectric signal of high intensity excites the voice coil- I'|,the speaker I6 produces a sound ofa certain intensity. Now if a sound of equal intensity; produced by some outside means, impinges on. the speaker I6, signal energy is rgeneratedu in the voice coil I'I, *which energy is relativelyfof -low intensity.

The amplier I9 is arranged to cooperate with the switch I8 so as to amplify weak signals corning through thewires 20 and 2|. to energize the voice coil I1,v or so as to amplify weak signals generated by the voice coil I'I for transmission through the wires 20 and 2i. In. orderftoaccomplish this result the switch I8 is provided with a rotary member having four equally spaced circumferential contacts 22, 23, 2d and 25, and with eight radial, equally spaced, stationary contacts arrangedV in pairs 26, 2'I; 28, 29; .30,.3I; 32, V33. 4An operating handle 34 is shown in `dotted lines in va position ycorresponding to the switch position shown` The'voice coil I l is connected between the fixed contacts 26 and 2l. rThe wires 20 and 2I are connected respectively to the fixed contacts 3|v and 30. A pair of .wires 35 and 36, which are connected to the input terminals of the amplifier I9, are connected respectively to the fixed contacts 32 and 33. A second pair of wires 31 and 38, which are connected to the output terminals of the amplifier I9, are connected respectively to the iixed contacts 28 and 29.

In the position shown the telephone apparatus is arranged for listening to signals coming over wires 20 and 2|. A circuit may be traced from wire 20 through switch contacts 3| 25 and 33, through wire 36 to one input terminal of Vthe amplifier I9 and from wire 2| through switch contacts 38, 23, and 32, through wire 35 to the other input terminal. The output terminals of the amplifier I9 are connected through a circuit which may be traced through wire 31, switch contacts 28, 22, and 26, through the voice coil I1 of the speaker I6, through switch contacts 21,24 and 29, and through wire 38 to the other output terminal of the amplifier I9.

In order to minimize cross talk between circuits, all circuits are arranged in balanced relation with respect to ground. A pair of equal resistors 39 and 40 are connected in series between wires 35 and 36l and their center point is by-passed to ground by a condenser 4|. In like manner, a pair of equal resistors 42 and 43 are .connected in series between wires 31 and 38 and their center point is by-passed to ground by a condenser 44. This arrangement maintains the circuits iny the telephone apparatus of station A balanced with respect to ground.

'I'he switching apparatus at station A; which provides controllable connections between the wires III, II; I2, I3; and2ll, 2|; comprises three switch buttons 45, 46, and 41, which cooperate with a latching arrangement, to be described later, which provides that upon depression of any one of the switch buttons the other two are released to an undepressed position. Each of these switch buttons is biased into an undepressed position by a spring, such as spring 48 in button 45. Each of these buttons is also provided with a pair of contact bridges, such, for example, as the contact bridges 49 and 59 of the button 45. In its depressed position the button 45 is arranged to make contact, by the contact bridges 49 and 50, from the wires 20 and 2| to a pair of wires 5| and 52. The switch buttons 46 and 41 are provided with similar contact bridges, which, however, are arranged to make contact between circuits both when the switch buttons are depressed and undepressed.

When the switch button 46 is depressed, a circuit exists from the wires 28 and 2| to a pair of wires 53 and 54, which are connected through an attenuation network `55 to the pair of wires I2 and I3 leading to station C. When the switch button 46 is undepressed, it is arranged to cornplete a circuit between the wires and 52 and the wires 53 and 54, respectively. It is therefore clear that, when switch button 45 is depressed, a circuit exists from the wires 29 and 2| through contact bridges 49 and 5U, through the wires 5I and 52, and the wires 53 and 54 through the attenuation network 55, and through the wires I2 and I3 to station C.

Similarly, circuits are arranged to be completed by the switch button 41 which in its undepressed position is arranged to complete a circuit between the wires 5| and 52 and wires 56 and 51 respectively. In the depressed position of the button 41 it is arranged to connect the wires 29 and 2| to the wires 56 and 51, which are connected through an attenuation network 58 to the wires I8 and II leading to station B. Thus, when the switch button 45 is depressed, the wires 28 and 2|, from which a circuit has been traced to the wires I2 and I3, which lead to station C, are also connected to the wires 56 and 51, and' through the attenuation network 58 to the wires I0 and II which leadto station B. It is, of course, to be understood that if more than three stations are provided in such a system, additional switch buttons similar to buttons 46 and 41 can be provided for connecting additional circuits at will to wires 5I and 52, or to wires 28 and 2|.

'Ihe operation of the telephone apparatus and switching arrangement, which form one of the stations of the system, may now be made apparent. With the parts in the positions shown, signals coming either through wires I0 and II, or wires I2 and I3, are transmitted through wires 5| and 52, and wires 20 and 2|, through certain contacts of the switch I8, through the amplifier I9, through other contacts of the switch I8, and to the voice coil I1 of the speaker I6 which reproduces the signals. Thus, vwith the switch button 45 depressed, station A is conditioned to reproduce signals coming from any other station.

If the switch button 46 is depressed, with corresponding release of the switch button 45, the wires 20 and 2| of station A are connected only to the wires I2 and I3. Therefore only signals coming from the wires I2 and I3 are reproduced in the speaker I6 and signals coming from the wires III and II have no eilect thereon. If, with the'switch button 46 depressed, the handle 34 of the reversing switch I8 be moved to its alternate position, as indicated by the dotted line 59, the speaker I6 translates sound into electric energy in the voice coil I1. A circuit is completed from the voice coil I1 through the reversing switch contacts 26, 22, 33, and 21, 24, 32, through wires 35 and 36 to the input terminals of the amplifier I9.` A circuit is also completed from the output terminals of the amplifier I9 through the wires 31` and 38, through the switch contacts 28, 23, 30, and contacts 29, 25, 3|, to the wires 28 and 2|.

Signals generated in the voice coil I 1 are therefore transmitted from the wires 20 and 2| through the depressed switch button 46 only to the wires 53,and 54 and through the attenuation network 55 to the wires I2 and I3. Thus, by moving the handle 34 of the reversing switch I8 between its two positions, the operator at station A may talk and listen alternately to the operator at station C. If the switch button 41 be depressed, with corresponding release of switch button 46, a similar private conversation may be carried on through wires I8 and with station B.

The function of the attenuation networks 55 and 58 will now be made clear. The wires I9 and I I are connected through an attenuation network 68 to the switching apparatus of station B, and `the wires I2 and I3 are connected through an attenuation network 6I to the switching apparatus at station C. The wires I4 and I5 are connected to stations B and C respectively by attenuation networks 62 and 63. The attenuation networks are all identical and are arranged so that the amount of attenuation produced in a signal passing through such networks, for example, through networks 5B and 60, is the same in amount as the amplification produced by ampliiier I9, or the corresponding amplifier at any other station. The amplifier I9 is arranged to amplify electric signals from a l'ow intensity, such as those generated in the voice coil I1, to a high intensity such as those required by produce sound.

Therefore, when the 'opera-tor: at station A is speaking, the voice coil I1 generates signal energy at low intensity.` The amplier I9 then amphi-les it to high intensity, and the attenuation networks 58 and 68 attenuate the signal energy again to low intensity, assuming that the switch button 41 is depressed. An amplifier 64 at station B, corresponding to amplier I9 at station A, amplifies the energy again to high intensity, so that a voice coil 55 at station B can translate the energy into` sound through the speaker 66.

Now atstation B it must be noted that the signal, coming from station A through the attenuation network 69, through a pair of wires 61v and 68, through the contact bridges of a switch button 69 in the switching apparatus of station B and through a pair of wires' 10 and 1I, also passes through the contact bridges of a switch button 12 and through a pair of Wires 'I3 and 14, through the attenuation networks 62 and 63 to station C. However, signal energy 'travelling by this path from station A through four attenuation networks in cascade to station C is of suchl low intensity upon arrival at station C that amplier 15 can only amplify the signal to a low intensity, such as is generated by the voice coil I1 when translating sound into electric energy. Since this low intensity is not sufficient to produce sound through speaker 16 at station C, there is effectively no signal transmitted to station C when the switch button 41 at station A is depressed.

The attenuation networks in the circuits between the stations therefore act as means to attennate signals transmitted therethrough sufliciently so that signals, passing from a station at which a call originated to a desired station and therefrom to a third station, are too greatly attenuated to effect the third station undesirably by producing sound. However, the quality of cornthe lvoice coil I1 to munication between two stations which are prop-Y erly switched together for conversation is not materially affected.

It should be noted that, by the use of attenuation networks so as to provide private communication, as for example, from station A tostation B, it is necessary only to depress one switch button 41 in order that signals from station A' be received only in station B. This effect is achieved through the use of the attenuation networks.

In addition to the three main stations A, B and C, which have been described, and any one of which is arranged so as to be able to call any other main station privately, there may be provided auxiliary or remote stations which mai7 communicate with the main station to which they are related. Since the auxiliary stations and their connections to their corresponding main stations are all identical, only one auxiliary station and its operation will be described. An auxiliary stationconnected with the main station A, for example, has'a speaker 11 with a voice coil 18 and a doublepole, double throw switch 19 which is spring-biased so as normally to connect the voice coil 18 to a pair of wires 80 and 8|. A switch button 82 in the switching apparatus at station A is arranged in its depressed position to connect the wires 89 and 8I respectively to the Wires 29 and 2|. If the switch 19 be moved to its alternate position, it acts to connect the voice coil 18 to a pair of wires 83 and 84, which'are respectively connected to the wires.5|.and.52. i ll 'I'heuoperation of this remote station is only possible .whenV the switch buttonsl 46 and l41 are undepressed. Assuming that 'station A is-'in a standby. position, in which the switch button 45 is depressed, the operator-at the speaker 11 may move the switch 19 `against its spring bias to connectr the .Voice coil 18 through thefwire 83 and 84,'and through the wires 5I and 52, the contact bridges 49 and 50, the wires 29 and 2l, through certain contacts of the reversing switch I 8, throughthe amplifier I9 and through other contacts of the switch I8 to the voice coil I1. When the operator at the speaker 11 speaks, signals are transmitted through this circuit and are reproduced by the speaker I6.

The operator at station A, may, if he desires, move the handle 34 to the position 59 and speak, so that th-e signal transmittedvfro'm station A effects the speaker 11,` aswell as the speakers at stations B and C.` If, however, the operator at station A desires to `speak privately with the auxiliary station, switch button 82 must be depressed and the handle 34 must be moved to p0sition`59. When this is done, :a signal from the voice coil I1 passes through. certain contacts of the switchlthrough` wires-35 and 36 to the input terminals of the amplifier I9, through wires 31 and 38 and'through other contacts of the switch I8 to the wires 29 and 2|, through the contact bridges of the switch 82 to the wires and 8| and, if 'the operator at the speaker 11 hasl released the switch 19, through the switch 19 to the voice coil 18. A two-way private conversation may then be carried on.

As many otherauxiliary stations may be associated with Station A, or with any other main station, as may be desired. For example, a second auxiliary station, including a speaker 85, is illustrated, which has a double pole, double throw switch 86 corresponding to switch 19 and a switch button 81 forming a part of theswitching apparatus of station A. The operation of this auxiliary station including the speaker 85 is identical withthe' operation described above for the other auxiliary station. Identical auxiliary stations including speakers 88 and 89 are illustratedin connection with station B and also auxiliary stations including speakers 98 and 9| in connection withstation C.

The attenuation networks act to provide private communication from an auxiliary station to its corresponding main station inmuch thesame way as they prevent signals Afrom passing from a desired main station to a third main station. That is, signal energy generated in the voice coil18, for example, is of low intensity and, although it is transmitted through the' wires 83 and 84 to the wires 5I and 52 and therefrom through the attenuation'neworks 55 and 58 to stations C and B respectively, the energy reaches stations B and C at such a very low intensity that the amplifiers 64 and 15 can only amplify j this energy to the' low, intensity at which it was generated in the voice coil 18, which is, as explained above, vinsufficient to produce sound in the speakers 66 and 16'. Since this energy from the voice coil 18. is transmitted to the amplifier of station A without having passed through attenuation networks, amplifier I9 can raise it to a high intensity suiiicient to produce sound in the speaker I6.

Although I have described my invention particularly as embodied in an interoice telephone system comprising main and auxiliarystations, it is to be understood that it is` useful'i'n any interccmmunicating system having no central switching station in which private communication between two stations of the system may be necessary or desirable. This system ,has the great advantage that when one station initially calls another station only the called station receives the signal. This result is accomplished merely by a single switching operation at the calling station.

As explained above, the switching apparatus at each main station is provided with means for maintaining a switch button in a depressed position, which means, upon depression lorf any switch butt-on, releases all switch buttons and thereafter locks the last one depressed in its depressed position. Fig. 2 illustrates a detailed view of a portion of such a means in which the switch buttons 46 and 41 are illustrated in cooperating relation with a latch bar 92. 'Ihe latch bar 92 is biased to the right by a spring 93 and is provided with slots 94 and 95 through which the shanks 96 and 91 of the switch buttons 46 and 41 respectively extend.

As illustrated, the switch button 46 is depressed and is maintained in depressed position by the latch bar 92 which cooperates withA a projecting portion 98 of the shank 96. A corresponding projecting portion 99 of the shank 91 is.y so arranged that, when the switch button 41 is depressed the portion 99 moves the latch bar 92 to the left against the force ofthe spring 93, so that the projecting portion 98 of the shank 96 is released and the switch button 46 moves under the influence of a spring 48 (Fig. 1) to its undepressed position. Upon slightly greater depression of the switch button 41, the projecting portion 99 moves completely beneath the latch bar 92, which thereafter moves to the right under the inuence of the spring 93 and in cooperation with the portion 99 locks the switch button 41 in depressed position.

It is to be understood that the latching mechanism for the switching operation which has been described is merely illustrative of one possible type of switching apparatus and its exact form is no part of the present invention. Other types of latching mechanism, such, for example, as are commonly used at the present time'in kradio receiver station selector switches, may be preferred.

While I have shown a particular embodiment of my invention, it will, of coursej'be' understood that I do not with to be limited thereto, since diierent modifications may be made both in the circuit arrangement and instrumentalities employed, and I aim by the appended claims to cover any such modifications as fall Within the true spirit and scope of my invention.

What I claim is new and desire to secure by Letters Patent of the United States is:

l. In a communicating apparatus, at least three intercommunicating stations, an independent communicating circuit extending from each of said stations to each of the other of said stations, means to connect each of said stations to all of said communication circuits extending thereto, means to disconnect one of said stations from all of said circuits except one circuit extending to a desired station, and means in each of said communicating circuits to attenuate signals transmittedk therethrough suciently so that signals passing from said one station to said desired station and therefrom to a third station are too greatly attenuated to aect undesirably said third station. v

2. In a communicating apparatus, at least three intercommunicating stations, an independent communicating circuit extending from each of said stations to each of the other of said stations, means to connect each of said stations to all of said communicating circuits extending thereto, means to disconnect one of said stations from all of said circuits except one circuit extending to a desired station, means in each of said communicating circuits to attenuate signals transmitted. therethrough suiiiciently so that signals passing from saidA one station to said desired station and therefrom to a third station are too greatly attenuated to aiect said third station, and means at each of said stations for amplifying said signals to their original value after attenuation in one of said independent communicating circuits.

3. In a communicating apparatus, at least three intercommunicating stations, each of said stations comprising a speaker for translating high level electric energy into sound and sound into low level electric energy and an amplifier for amplifying low level electric energy to high level electric energy, an independent communicating circuit extending from each of said stations to each of the remaining one of said stations, means to connect each of said stations to all oi said communicating circuits extending thereto, means to disconnect one of said stations from all of said circuits except the circuit extending to a desired station, and means in each of said communieating circuits to attenuate signals transmitted therethrough from a high level to a low level so that signals passingfrom said one station to said desired station are transmitted therefrom to a third station at so low a level that the ampliiier and speaker at said third station are not alTected.

4. In a communicating apparatus, a plurality of intercommunicating main stations and an auxiliary station, each of` said stations comprising a speaker for translating high level electric energy into sound and sound into low level elecric energy and an amplifier for amplifying low level electric energy to high level electric energy, an independent communicating circuit extending from each of said main stations to each of the other of said main stations, means to connect each of said main stations to all of said communicating circuits extending thereto, means to disconnect one of said main stations from all of said circuits except the circuit extending to a desired main station, means in each of said independent communicating circuits to attenuate signals from a high level to a low level, and means for disconnecting each of said main stations from all communicating circuits and for connecting said main station to said auxiliary station through said amplifier for private communication therebetween.

HUBERT R. SHAW. 

